Cutting knives have a very ancient and long continuous history. A cutting edge has been traced back to the Stone Age when hard rock was sharpened to a fine edge for cutting and scraping and later this concept developed into a metal implement with a sharp cutting edge. In the course of this history there have been continuous developments right up to the present time. Obviously any invention at this time must be played against this vast chain of development and must be significant in order to be useful.
Possibly the three most important considerations in knife development are safety, balance and convenience. All of these must include esthetics, as an ugly or awkward instrument presenting any difficulty would be useless and unsalable.
Amongst the most recent art which has developed with respect to knives includes the U.S. Patent to Paul W. Poehlmann, No. 3,942,249, which issued Mar. 9, 1976. While the knife described and disclosed therein had the germ of a useful improvement, the form described and disclosed in the patent is utterly incapable of being manufactured reasonably and competitively as it has built in inherent characteristics which doom the structure to mechanical failure. It is difficult to operate and is dependent upon springs which are notorious bad actors so far as reliability and calculated life are concerned.
In order for a knife to be useful it must possess certain advantages. One of these advantages is that it must be capable of commercial manufacture using standard tooling which are not only easily available but are the ordinarily used tools of a competent metalworker. No special or exotic tooling or machinery should be required for the manufacture.
It should operate using a familiar conventional technique to open and close the knife, so that the user does not have to learn a new technique or knack of performing this simple operation.
Because of the unreliability of springs, whether coil or leaf, and the lack of uniformity of performance, the use of springs should be eliminated. However, a relatively heavy pressure of 12 to 14 psi should be provided for the release of any locked position of the blade to prevent any chance of accidentally unlocking the blade whether in the open or closed position.
In releasing the lock holding the position of the blade, only a minumum movement of the release mechanism should be required.
A locking mechanism should provide a minimum overall size to allow for the most compact design of the knife. The release and locking mechanism should be small enough so that it can be standardized for use in the greatest number of knife sizes, without reducing or enlarging the basic size of the mechanism.
The moving parts in the mechanism with the exception of the plunger head should be concealed from any outward view, not only for the purpose of esthetics but for the very practical reason of insuring against the entry of dirt and contaminants which would interfere with the safe operation of the locking mechanism.
The matching slots in the blade and liner which can be planned in any position in a plane, so long as they are aligned with each other.
Obviously the blade must be capable of being locked in both the closed and open positions.
A very important maintenance object is, if the blade loosens from excessive wear, the lateral play will be easily eliminated by tightening the lock ring. If necessary the lock ring can be fixed in position with the material known as Loctite. However, since it is not subjected to any motion, mechanical locking of the ring is not necessary.
In order to reduce any likelihood of wear both the locking bar and blade must be of the same type steel and Rockwell hardness.
Another feature which is an objective is to provide a knife which is quieter and does not make any loud "click" when moved from the closed to the open position as is true with practically all knives of this character.
Design features of the knife are important in limiting the rotating parts to one, which is the blade, and two movable parts to two the plunger assembly and the locking bar.
The elimination of spring pressure on the blade which must be overcome when opening, does away with the necessity for the thumb nail nick, and the absence of spring pressure against the blade results in greater leverage allowing tighter or closer fits in the entire construction.
A little known advantage is attained by the structure herein in the elimination of the flat area of the blade between the bevel and the handle where the trademark is usually stamped into the metal, called the "ricasso". This also provides the greatest operative length for the cutting edge resulting in a stronger and more usable blade, and improves the esthetic characteristics of the entire knife.
It is a further object of this invention to cut down the maximum thickness through the bolsters, resulting in a much thinner or flatter knife than that of conventional and comparable knives.
All of these are the advantages and objectives attained by the structure disclosed herein.
Further objects are to provide a construction of maximum simplicity, economy and ease of assembly and disassembly, also such further objects, advantages and capabilities as will fully appear and as are inherently possessed by the device and invention described herein.
The invention further resides in the combination, construction and arrangement of parts illustrated in the accompanying drawings, and while there is shown therein a preferred embodiment thereof, it is to be understood that the same is illustrative of the invention and that the invention is capable of modification and change and comprehends other details of construction without departing from the spirit thereof or the scope of the appended claims.